During the drilling of a well, gas or oil for example, drilling mud is typically pumped down the drill string through a drill bit. The drilling mud simultaneously cools the bit and carries drill cuttings up the well bore. Drilling mud is typically comprised of a fluid (or fluids), and mixture of additives which can be either fluids or solids, forming a useable drilling fluid. Oil based or brine based drilling fluids are often used to drill oil and gas wells because they have special characteristics that make them a better cooling/carrying fluid than other drilling muds. Additionally, such drilling muds may offer better wellbore stability and/or lubricity for the drill string in modern, horizontal wellbores.
Typically, the drill cuttings which are carried up the wellbore are subjected to solids separating devices when the cuttings exit the wellbore, such as that of shale shakers or decanter centrifuges. These mechanical separators allow a substantial portion of the drilling mud to be returned to the storage tanks for reuse, while the drill cuttings portion is sent to separate storage tanks. The drill cuttings still contain residual amounts of the drilling mud that couldn't be separated through mechanical means, and this residual drilling mud is considered to be contamination.
The drill cuttings are commonly known as drilling waste, because they serve no purpose after they have been removed from the wellbore. Thus, the contaminated drill cuttings are typically stabilized with a bulking agent, such as fly-ash, sawdust, or liquid absorbing pellets, to prevent residual free liquids from leaching from the solids during transport. The cuttings are then typically transported to a secure landfill where they are stored for an indeterminate period of time, typically generations.
It is not an uncommon job site practice to throw refuse, for example drilling mud bags, spent plastic sheets or broken pallets into the onsite drill cuttings storage bin. This practice has not been seen as problematic because the drilling waste was destined for a landfill.
With the evolution of new technologies and the increasing cost of drilling fluids, the ability to, and benefits of, reclaiming the lost drilling fluids is increasing. However, technologies such as thermal extraction, solvent washes, or alternate mechanical separators work less effectively, if at all, with bulking agents or refuse mixed with the drilling waste, prior to shipping.
Typically, stabilized drill cuttings are loaded into open top, sealed end dumps and then moved to a secure waste landfill. A sealed end dump is a large open trailer which allows the material to be moved by loader or excavator into the trailer, while the sealed nature of the end dumping gate ensures any transient liquids that are able to leach from the stabilized drill cuttings, remains in the trailer during transport. A tarp or net is moved over the load to ensure that a minimum amount of moving air is in contact with the stabilized drilling waste, including the refuse when present, preventing it from becoming airborne and leaving the trailer.
This has proven to be a convenient and economical way to transport stabilized drill cuttings. However, the use of this type of transport vessel, which has become an industry standard for transporting drilling waste, is not a practical way to transport unstabilized drilling waste, especially because of potential safety issues. For example, if bad road conditions, driver error, or other adverse circumstances, contribute to an accident, or cause trailer over-turning, the load could easily flow out of the transport vessel onto the ground or otherwise end up in a water-way. The flammable or toxic nature of the oil base or brine base drilling mud contaminating the drill cuttings could cause significant environmental damage or even loss of life.
Thus, the need to transport unstabilized drill cuttings in a safe, efficient manor to recycling or remediation facilities has arisen.